The invention relates generally to the field of photography, and in particular to cameras. More specifically, the invention relates to a camera in which aperture adjustment for an objective lens is accomplished using a shaped memory alloy driver.
Prior art U.S. Pat. No. 5,279,123 issued Jan. 18, 1994 mentions that shaped memory alloy (abbreviated to SMA) devices are well known in the art to undergo a martensitic (diffusionless) transition dependent upon the temperature applied to the SMA device. The SMA device when heated above its transition temperature undergoes a shape change to a memorized shape and when cooled below its transition temperature reverses the shape change from the memorized shape to an original shape. This change in shape can be used to provide mechanical work.
Often, as disclosed in prior art U.S. Pat. No. 5,459,544 issued Oct. 17, 1995, the SMA device is a fine metallic wire. When electrical current is applied to lead wires connected to opposite ends of the SMA wire, the SMA wire is heated to due to electrical resistance and it shrinks or contacts, i.e. recovers, to a memorized shape. When the electrical current is discontinued, the SMA wire cools to extend, i.e. deform, to an original shape. One application of the SMA wire to do mechanical work in U.S. Pat. No. 5,459,544 is a lens displacing mechanism for an objective lens, including an actuator pivotable in opposite directions to displace the objective lens in respective directions and an SMA wire which when heated contracts to its memorized shape to pivot the actuator forward to displace the objective lens forward and when cooled extends to its original shape to allow a return spring to pivot the actuator rearward to displace the objective lens rearward. The objective lens is displaced between two extreme positions, a close or near focus position and a far or infinity focus position, to change the actual distance between the lens and the film plane in a camera in order to adjust the image sharpness. Another application of the SMA wire to do mechanical work in U.S. Pat. No. 5,459,544 is an aperture adjustment mechanism, including an aperture blade which has a large diameter hole and a small diameter hole and which can be translated in opposite directions to move either one of the holes into optical alignment with the objective lens, a cantilever leaf spring that is connected to the aperture blade between the two holes and that can snap in opposite directions to alternative stable positions to translate the aperture blade in opposite directions, and a pair of SMA wires that are connected to the leaf spring and when alternately heated to contract to their memorized states urge the leaf spring to snap to its respective stable positions.
The cross-referenced application discloses a camera control mechanism comprising an actuator movable to adjust an adjustable component, such as for lens focusing or aperture adjustment, and a shaped memory alloy (abbreviated to SMA) wire which when heated contracts to a memorized shape to move the actuator to adjust the adjustable component. The SMA wire has opposite ends that are fixed in place and an intermediate movable portion between the opposite ends that directly contacts the actuator to move the actuator when the SMA wire is heated to contract.
According to one aspect of the invention, a camera adapted to receive any one of a plurality of film loads having different film speeds comprises:
a film speed sensing device for sensing the particular film speed of a film load in the camera;
an aperture setting device adjustable to effect different-diameter film exposing apertures;
a shaped memory alloy (abbreviated to SMA) wire which when subjected to electrical current for different durations corresponding to the respective film speeds of the film loads is heated to undergo corresponding shape changes to adjust the aperture setting device to the respective film exposing apertures; and
a current supplying circuit connected to the SMA wire and to the film speed sensing device that subjects the SMA wire to electrical current for any one of the durations in accordance with the particular film speed of a film load in the camera.
According to another aspect of the invention, a method of adjusting an aperture setting device to effect different-diameter film exposing apertures in a camera adapted to receive any one of a plurality of film loads having different film speeds comprises:
sensing the particular film speed of a film load in the camera; and
subjecting a shaped memory alloy (abbreviated to SMA) wire to electrical current for different durations corresponding to the respective film speeds of the film loads, to heat the SMA wire to cause it to undergo corresponding shape changes and adjust the aperture setting device to the respective film exposing apertures in accordance with the particular film speed of a film load in the camera.